Deck Board Calculator
Turn a deck area into a board count. Enter the square footage and your board size, add a waste allowance for cuts and trimming, and get the number of deck boards to buy.
Calculator
A 200 sq ft deck in 5.5 in × 8 ft boards, with 10% waste, needs about 60 boards. Diagonal or picture-frame layouts waste more; each board covers its face width (nominal 6-in boards are ~5.5 in).
Decking is sold by the board, but you plan by the square foot, so the take-off comes down to how much surface one board covers. That coverage is the board's actual width times its length — and a "6 inch" board is really 5.5 in wide, so using the nominal name would short you on material.
Add a waste allowance on top: every deck loses boards to end cuts, board matching and the odd split, and diagonal or picture-frame layouts lose more. Enter your real area and board size and the tool rounds up to whole boards you can actually buy.
Formula
One board covers its width (in feet) times its length; boards come from the area plus waste divided by that coverage:
board_coverage = (board_width_in ÷ 12) × board_length_ft boards = ceil(area_sqft × (1 + waste%) ÷ board_coverage)
Dividing the width by 12 converts inches to feet so the coverage lands in square feet. The ceil() rounds up because you buy whole boards. This counts the decking surface only — joists, beams, railing and fascia are separate lumber.
Worked example
A 200 sq ft deck built from 5.5 in × 8 ft boards with a 10% waste allowance:
- Board coverage: (5.5 ÷ 12) × 8 = 0.4583 × 8 = 3.667 sq ft per board
- Area with waste: 200 × 1.10 = 220 sq ft
- Boards: 220 ÷ 3.667 = 60.0 → 60 boards
So 60 boards cover the field of a 200 sq ft deck with a 10% cushion. Add fascia, stair treads and any pattern boards separately, and pick up a couple extra so you are not short on the last row.
Decking take-off in practice
Use the real width. Dressed 5/4×6 and 2×6 deck boards measure 5.5 in wide; composite boards are often 5.5 in too, but some run 5.375 in or 7.25 in — check the spec and enter the actual figure, because a small width error multiplies across a whole deck. The tiny gap between boards is usually ignored in the count and absorbed by the waste allowance.
Waste by layout. A straight deck laid in one direction wastes the least (about 5%). Diagonal decking, a picture-frame border and short or busy stock all push waste toward 10–15% because of the extra angled cuts and offcuts you cannot reuse. Pick the waste band that matches your plan.
Board length. Choosing a stock length that divides evenly into your deck runs cuts waste sharply — a 16 ft deck built from 16 ft boards has almost no end-cut loss, while the same deck from 12 ft boards forces a seam and more offcuts. Where you can, buy to the run.
Fasteners. Two screws per board at each joist is the rule of thumb; at 16 in joist spacing that is roughly 350 screws per 100 sq ft of deck. Hidden-fastener systems clip per linear foot of board instead — follow the system's coverage. Price the whole build with the deck cost calculator.
Reference table
Coverage per board (width ÷ 12 × length) for common sizes — before waste:
| Board size | Covers |
|---|---|
| 5.5 in × 8 ft | 3.67 sq ft |
| 5.5 in × 12 ft | 5.50 sq ft |
| 5.5 in × 16 ft | 7.33 sq ft |
| 7.25 in × 16 ft | 9.67 sq ft |
Nominal 5/4×6 and 2×6 boards are 5.5 in wide; confirm the actual width on the product spec.